Strange noise, a bad day NOW Good
 

Hi,

Yesterday was a bad day, after getting a fix-it ticket for no front plate and a warning for speeding (well, that wasn't so bad after all). After filling the tank with gas, i pulled up to a stop sign, then started off. But something strange happenned.

The engine lost some power, and started to make a very loud throaty noise. i checked and it is not coming from the exhaust side, but seems to be from the intake side, on cylinder 1-3 (passenger side).

Could it but something simple like a plugged jet? Or is it worse? I am not sure if there was a click/clunk/thud when i stopped. And the noise is very loud on accerlating, but hardly there on constant throttle. Doesn't seems to be any odd mechanical noises. :confused:

i haven't had time to look at it since, and it is driving me nuts. The engine is a 2.0 with solex cams, freshly rebuilt -250 miles, the webers are not 100% dialed in yet though. Any comforting thoughts or ideas?

Stuart

Stuart,

Assuming that you are still using the stock air filter housing ... is it possible that some or all of the 'overcenter' retaining clips came loose on the passenger side of the air cleaner that clamp it to the top of the right carb?

The noise is puzzling. But you'd "just" filled with gas?

i can check that the filter is still on correctly, the clips are not as tight as they could be. Yes it its original. But if it is loose, why the loss of power?
Gas? yes, 12 gallons of Chevron 91 ocatane. Drove about a mile tops before this happenned.

Stuart

The air cleaner system on an early 911 engine is part of the tuning that matches the cams, equal-length headers inside the heat exchangers, and the intake tract tuning that extends from the intake valves all of the way to the long inlet horn of the air cleaner assembly ...

So, if the right side of the housing popped off/loose, you suddenly upset the pressure waves involving intake reversion pulses that extend above the velocity stacks of the Webers ... and that sudden change probably upset the torque that was being delivered, and the responsiveness of the engine to throttle inputs.

The intake noise increase on one side is the best clue I have ... and, torque produced at the bottom end will be higher with air cleaner properly seated, sealed, and with the intake horn in place,as opposed to just open Webers with nothing above the velocity stacks!

Flash update:

All 10 clips are securely fastened. Much as i liked the airbox-came-loose theory, it doesn't seem to fit today.

After supper, and when all is quiet here (like late tonite), i can poke about some more.

Stuart

Flash update number 2

Well Xmas came and went, so did new year, the car sat in the garage while i traveled to and about Melbourne, saw Porsche #1.
Came home, pulled air cleaner, started car. Very massive amount of fuel being blown up cylinder #1. Checked carb for stuck float valve, and level hoping that it was just dumping fuel into the cylinder and running very rich. Start up, still massive popping out #1.
Pull exhaust valve cover thinking broken rocker/valve (spring) was that click sound i think i heard. No such luck, the rocker shaft had wandered out, leaving the rocker to sit there. Damn, that is the second one, same rocker position, different side (no. 6 wandered out too). Cleaned and replaced rocker and shaft, tightened as much as possible, runs fine again. Other shafts are fine.

Anyone heard of these end shafts floating out?
What tool do you use to tighten the rocker shafts, are there shorted allen keys or sockets available, my 8mm is kinda too big to get a reaally good grip.

Stuart

the factory torque is insufficient. use 18#. the 8mm end is held with a cut off allen wrench while you tighten the 5mm end. 1/4 drive torque wrench and real short 5mm allen socket. do you know the proper position for the shafts? tightening the shafts in the wrong position can cause leaks as well as the shaft walking out.

We're pretty lucky. I dropped into the Porsche Centre Melbourne yesterday to get some spares and drooled over the Paris-Dakar 3.2 Carrera Allrad among other significant Porsches.

Pity all heitage and engineering excellence is lost on the hordes of latte-drinking, bohemians that filled the place, negotiating on tiptronic Boxsters...

To Mr. Walker's question, i use the feeler guage plus 1.5mm technique to locate the shaft in the housing. They were all torqued to factory when i assembled the motor, but i will have to cut an allen to do them again.

Yes you are pretty lucky in Melbourne, when i was at PCM it must have been noonish with noone around. It was nice to take photos of all the "museum cars" without being asked if i needed help. i almost opened the door to Number 1 and sat in it, but decided against it.

Talking as someone whose engine is in a bunch of ziplock bags at the moment, that is a good thing to know.

Tom

Hang in there, Tom!
In a few more weeks, you'll get a *great* feeling as you start emptying all those baggies. :)

The last time I heard a strange noise, it was the prelude to installing engine #3. If it was a USA push-rod engine it would have been a broken or loose rocker arm - same sound. Or maybe a spark plug fallen out of the cylinder head. But - it was a 2.7L; when the timing chain cover was pulled, little bit of oddly shaped metal fell out. I closed her up and administered last rights. "Honey - where's my checkbook?"

this may be a shot in the dark........but could one of your spark plugs backed out a little? i've had that happen once and it made a similar noise.
my .07